1. Field of the Invention
The present invention relates generally to a control system for an automotive automatic power transmission which can adapt shifting timing of the transmission to a driver's feeling utilizing fuzzy logic. More specifically, the invention relates to an intelligent control system for an automatic power transmission adapting an automated transmission shifting pattern to a vehicle driving pattern of a specific driver. Further particularly, the invention relates to a transmission shifting control system with refined learning and recollection characteristics for updating parameter data and selecting a shifting pattern based on input parameter data.
2. Description of the Background Art
In the modern automatic power transmission control systems, electronic control units have been employed for precisely and optimally controlling shifting of the automatic power transmissions. Some modernized transmission control systems employ variable shift pattern strategy for adapting transmission shift patterns to vehicle driving patterns which are determined generally based on vehicle speed and throttle valve angular positions. For example, Japanese Patent First (unexamined) Publications (Tokkai) Shows 59-200845 and Showa 59-200848 disclose transmission control systems which employ shifting tables containing a plurality of transmission speed ratio shifting patterns.
Tokkai Showa 59-200845 discloses a transmission control system which has two transmission gear shifting pattern maps. One map is directed to a general shift pattern to be used in usual traffic. The other map is directed to a special shift pattern for extraordinarily heavy traffic. The proposed system utilizes a throttle pedal depression pattern as a parameter for selecting one of two transmission shifting pattern maps. On the other hand, Tokkai Showa 59-200848 discloses a similar transmission control system for selectively using transmission shifting pattern maps. In the proposed system, longitudinal acceleration is used as a parameter for selecting one of the maps.
In either case, the prior proposed transmission control systems employ a singular parameter for selecting shifting pattern maps. In such a type of transmission control, the selected parameter is compared with a predetermined criterion for selecting one of the preset transmission shift patterns. This encounters drawbacks because the singular parameter does not always represent an actual driving condition. That is, in practical control, failure of detection of the driving condition may cause erroneous selection of the inappropriate shifting pattern and degrading drivability of the vehicle.
On the other hand, some of the prior proposed automatic power transmission shifting control systems employ microprocessor or microcomputer based control modules. The control module stores data in a form of maps relative to various kinds of shift patterns including a power pattern where an acceleration performance is emphasized and an economy pattern where fuel economy is emphasized. Sensor output signals from a throttle sensor and a vehicle speed sensor are supplied to the control module. Based on the sensor signals, the control module performs a selected operation among the above-mentioned maps and then a look-up operation for the map is selected to retrieve transmission ratio data arranged in the map versus throttle open angle and a vehicle speed indicated by the sensor signals. The control module generates a shift signal indicative of the transmission ratio obtained. In this manner, a fine selection among transmission ratios is made to determine a transmission ratio most suitable for a driving condition of the vehicle.
With such a known control system, the plurality of maps are provided and selected in accordance with various vehicular driving conditions. There occur events where a shift between transmission ratios is made in accordance with an inappropriate shift schedule which is not adapted to the vehicular driving condition. This is where an improvement needs to be made. If all shift points fit for all available driving conditions of the vehicle were to be set, the number of maps would be considerably increased. Therefore, it is common practice to limit the number of shift patterns, each being fit to one of the representative driving conditions.
In order to solve the problem set forth above, the co-pending U.S. patent application Ser. No. 07/175,350, filed on Mar. 30, 1988, and assigned to the common assignee to the present invention, proposes an automatic power transmission control system employing fuzzy-logic. According to this prior proposal, fuzzy-logic is employed in order to determine a transmission ratio suitable for vehicle driving conditions. In the fuzzy-logic control module, a series of membership functions are referred to based on a series of signals representative of the vehicle driving conditions. The membership functions are fixed once they are set, so that it is impossible to provide shift characteristics with sufficient flexibility to cope with different drivers' driving behavior and different environments in which the automotive vehicle may be involved.
Further prior proposals have also been made in U. S. Pat. No. 4,777,585, issued on Oct. 11, 1988 to Kokawa et al, for the invention relating to "Anological Inference Method and Apparatus for a Control System"; and U.S. Pat. No. 4,809,175, issued on Feb. 28, 1989, to Hosaka et al. for the invention relating to "Vehicle Control System and Method Therefor".
These prior proposals also employ fuzzy logic for adapting a transmission speed ratio selecting schedule or pattern to the drivers' feeling or vehicular driving pattern. In addition, the co-pending U.S. patent application Ser. No. 7/309,442, filed on Feb. 13, 1989 now U.S. Pat. No. 5,019,979, which has been commonly assigned to the assignee of the present invention, discloses "Control for Automatic Transmission", in which there is disclosed a fuzzy logic controlled automatic transmission of an automotive vehicle comprising a series of detectors for detecting parameters indicative of the vehicle driving conditions and generating a series of detector signals indicative of the parameters detected. A fuzzy logic control module contains a series of rules of thumb, each being expressed by a series of membership functions of the detector signals and recommending a position which the automatic transmission should take. In the fuzzy logic control module, the series of rules of thumb signals to determine the degrees to which the series of rules of thumb are satisfied, and a position which the automatic transmission should take is determined. An output signal is generated by the fuzzy logic control module which is indicative of the position determined. A modifier is provided which changes or modifies at least one of the series of membership functions of at least one of the series of rules of thumb when the history of at least one of the series of detector signals shows a predetermined state. Another proposal has also been made by the common assingee to the present invention in the co-pending U.S. patent application Ser. No. 7/375,970, filed on July 6, 1989, which relates to an invention "Shifting Control for Automatic Power Transmission with Learning Shifting Pattern Model and Selecting Shifting Pattern Model from Closest Vehicular Driving Pattern", in which it is disclosed that a transmission gear shifting control system is selective of speed ratio of an automotive automatic power transmission. The control system employs a strategy of learning of driving conditions in order to select one of a plurality of vehicle driving patterns so as to adapt to the vehicular driving condition and the driver's desire, by means of a neuron computer. The system monitors a plurality of vehicle driving parameters and stores driving pattern data in an associative storage for forming stored driving patterns. The driving pattern data is stored in terms of relevant one of a transmission gear shifting patterns so that the transmission gear shifting pattern can be selected in response to entry of the stored relevant driving pattern. The control system is further operable for associatively recollecting one of the driving patters on the basis of the monitored driving parameters and stored driving patterns.
The last mentioned prior proposal made by the common assignee to the present invention incorporates a neuron computer system known as an "ASSOCIATRON". In bries, concerning this ASSOCIATRON, the logic of the "ASSOCIATRON" has been proposed by Doctor Nakano of Tokyo University and discussed in "Information System in Brain formed by Basic", published by Keigaku Shuppan K.K. on Mar. 30, 1988, pp17-29. Discussion concerning the "ASSOCIATRON" will be herein incorporated by reference thereto for the sake of disclosure.
The logic of the "ASSOCIATRON" generally includes patterning of received information, writing of patterned information in an associative storage and recollecting information from the associative storage. The "ASSOCIATRON" utilizes associative storage model as shown in FIGS. 8 and 9. The associative storage model contains a plurality of storage elements Xi (i=1, 2, 3 . . . ) arranged in a form of a storage array and associated with adjacent storage elements via information transfer elements Mi. In the logic of the "ASSOCIATRON", each of the storage elements Xi is referred to as a "neuron". Therefore, in the following disclosure, the word "neuron" is used for representing a storage element in an associative storage model in the "ASSOCIATRON". Also, the information transfer elements Mi (i=1, 2, 3 . . . ) connecting the neurons Xi are each referred to as a "synapse" in the "ASSOCIATRON". Therefore, in the following discussion, the word "synapse Mi" will be used for representing the information transfer elements. Each neuron Xi is variable in state amount 1, be appreciated herefrom, according to the recollection input pattern of FIG. 12, the excitation pattern of FIG. 11(b) is the closest. As can be seen from FIG. 11(b), the stored pattern contains excited neurons X.sub.4, X.sub.8, X.sub.9, X.sub.12, X.sub.14, X.sub.16, X.sub.17, X.sub.18, X.sub.19, X.sub.20, X.sub.24. Therefore, in the associative recollection according to the "ASSOCIATRON", the neurons X.sub.12, X.sub.18, X.sub.20 and X.sub.24 are assumed as excited and thus a figure pattern of four (4) is recollected in response to input of the recollection input pattern of FIG. 12.
By utilizing the strategy in the "ASSOCIATRON" as set forth above, patterning of the vehicular driving patterns and recollection utilizing stored patterns in the associative storage and "ASSOCIATRON" logic for associative recollection, the automatic power transmission gear shifting pattern adapted to the vehicular driving pattern is selected.
The prior proposed system set forth above is capable of adpating the transmission shifting pattern to the driver's feeing by learning a shifting pattern and associated vehicular driving condition utilizing the logic of an ASSOCIATRON. On the other hand, in such a system, updating of map data takes place whenever transmission gear shifting is commanded. This prevents associative recollection. In general, demand for recollection arises when variation of the transmission speed ratio is required due to a change of the vehicular driving condition. In such an occasion high response to the speed ratio variation demand is desired so as to prevent the engine performance from being degraded due to low response characteristics.